The positive-working photoresist composition of the present invention comprises an improvement in the composition disclosed in U.S. patent application Ser. No. 07/125,278, filed Nov. 26, 1987, the disclosure of which is herein incorporated by reference.
Positive-working photoresist compositions generally comprise a composition containing an alkali soluble resin and a light-sensitive substance of naphthoquinonediazide compound. For example, U.S. Pat. Nos. 3,666,473, 4,115,128, 4,173,470, etc., describe "novolak type phenolic resin/substituted naphthoquinonediazide compound", and L. F. Thompson, Introduction to Microlithography (ACS, No. 219, pp. 112-121) describes an example of a "novolak resin composed of cresolformaldehyde/1,1-naphthoquinonediazidesulfonate of trihydroxybenzophenone" as the most typical composition.
Novolak resins used as binders are particularly useful for this use, since they can be dissolved in an alkaline aqueous solution without swelling and, when a resulting image is used as a mask for an etching process, they provide a high resistance particularly against plasma etching. Naphthoquinonediazide compounds, which themselves function as a dissolution-preventing agent to reduce alkali solubility of the novolak resin, are peculiar in that, when decomposed by irradiation with light, they produce an alkali-soluble substance which increases the alkali solubility of the novolak resin. Naphthoquinonediazide compounds are particularly useful as light-sensitive substances for a positive-working photoresist due to the above-described great change in properties to be caused by light.
Many positive-working photoresists containing a novolak resin and a naphthoquinonediazide light-sensitive substance have so far been developed and put into practice from the above-described point of view, and sufficient results have been obtained in working with a line width of about 1.5 .mu.m to 2 .mu.m.
However, the degree of integration of IC circuits has been increasing more and more and, in the manufacture of semiconductor bases for super-LSI, etc., working of superfine pattern composed of line with a width of up to 1 .mu.m has been required In such uses, photoresists having high resolving power, high pattern-reproducing accuracy capable of accurately reproducing an exposure mask image, and high speed in view of high productivity have been required However, the above described conventional positive-working photoresists fail to meet these requirements.